Gas mixing apparatus



July 16, 1957 P. KNIGHT 2,799,288

GAS MIXING APPARATUS Filed Dec. 20, 1954 INVENTOR. P. L. KNIGHT---ATTORN United States Patent GAS MIXING APPARATUS Philip L. Knight,Toledo, Ohio, assignor to Surface Combustion Corporation, Toledo, Ohio,a corporation of Ohio 4 Application December-.20, 1954, SerialNo..4'7.6,2 65

8-Claims. (Cl. 137-98) This invention relates to gas mixing apparatus ofthe type having orifices in the respective air and gas lines in whichsubstantially equal gas and air difierential pressures over theseorifices are maintained to obtain proportioning of the gas and the fuel.

It is known that orifices, and venturis (which area special class oforifice) have characteristic flow rates roughly proportional todifferential pressures therethrough for a given gas and venturi size anddesign. 'These characteristics are extremely di-fficult to actuallyduplicate in a given size, or to match for proportioning, and inpractice it has been found impractical to maintain large .turndown withsuch mixing apparatus. This invention provides the means for solving theproblem ofextending the turndown range of a mixing apparatusincorporating gas and air orifices which are used to proportion the flowof gas and air.

Fora consideration of what I believe to be novel and my invention,attention is directed to the following portion of the specification andthe drawingand the claims thereof.

The drawing shows a schematic diagram of apparatus according to thepresent invention.

In the apparatus illustrated, air is supplied at a substantiallyconstant pressure by a blower 11 to an .air pipe 22 and is passedthrough a venturi 12 which is aprimary, fixed restrictor andtherethroug-h to a mixing T 1 3. Fuel gas is supplied through a gas main16 and a regulator 17 which is back loaded by a pipe 21 to the air pipe22 in such a manner such as to produce substantially constant gaspressure which may be equal to or a slight variance to the air pressure.The gas then passes through pipe 16 to a gas venturi 18 which also is aprimary, fixed restrictor, through a variable orifice valve 19, and tomixing T 13. The gas mixture passes from the T 13 through a pipe 14 andmixture flow valve 15 and thence to burners, not

shown, for consumption. A temperature control device 25, ordinarilyresponsive to a thermocouple in a furnace, controls a servo-motor 24 tooperate a push rod 23. The mixture flow valve 15 is operated from thepush rod by a linkage 26. Push rod 23 also operates a cam member 27 inthe valve 19 so that as the push rod 23 moves the valve 19 is alsomoved.

The valve 19 which is a secondary adjustable restrictor is a relativelycommon type which may be characterized in such a manner as to make thedegree of opening of the valve directly related to but not proportionedto the travel of the push rod 23 or degree the valve stem is turned.This is ordinarily done by a set of adjusting screws which are adjustedto change the shape of a valve operating cam on the under side of themember 27. Such a valve is illustrated in a Patent to F. T. Cope, Number2,341,177.

In the original setting up of the apparatus illustrated, the burnerswill ordinarily be set to fire at a maximum rate and the gas and airventuris will be selected to produce a substantially perfect air-gasmixture. The burners will then be reduced in firing rate by steps and ateach step the valve 19 will be adjusted in a manner to change thecharacteristics of the gas venturi 18 by increasing or decreasingresistance to gas flowsufficient tomaintain the air-gas ratiosubstantially constant. ,After this has once been done over the fulloperating range of the apparatus, then for every position of the gasmixture valve, which corresponds to a rate of flow of mixture to theburner, there is a corresponding position andadjustment of the variableorifice valve 19 which will correct the characteristics of the gasventuri 18 in a manner to produce with the air venturi 12 a constant airgas ratio.

If it is desired to operate this apparatus asa mixing station to producea constant pressuremixture for supplying fuel to a multiplicity offurnace zones, the temperature controller instrument 25 may be replacedby an instrument responsive to gas pressure downstream of the valve 15and will thus open and close the valve 15 in a manner to maintain aconstant pressure downstream thereof.

It will .be appreciated that the valve 19 may be upstream or downstreamat the gas venturi 18, or a larger size valve equivalent to the valve 19might be placed in the airpipe 22, so that the air venturicharacterization would be adjusted instead of the gas venturi.

I claim:

1. Fluid mixing apparatus comprising: a plurality of fluidconduits-delivering into a common fluid mixture conduit; a mixture flowcontrol valve in the mixture conduit; a primary, fixed restrictor ineach of said fluid conduits which restricts flow therein and maintain anapproximately constant ratio of flows through said conduits for variousrates of total flow; a secondary, adjustable restrictor in each saidfluid conduits except one; means for controlling the relative fluidsupply pressures to said fluid supply conduits; and means linking saidmixture fiow control valve to said secondary, adjustable restrictors toactuate them in fixed relation whereby at any opening of said valve theratio of'flovvs through the conduits containing the primary restrictorsis maintained substantially constant.

2. Fluid mixing apparatus for supplying a combustible mixture of fueland air .to burners, comprising: an air conduit and afuel conduitsupplying, respectively, .air and fuel to a mixture conduit which inturn is adapted to supply combustible fuel and air mixture to theburners; a primary, fixed restrictor in the fuel conduit and the airconduit which restrict fiow in their respective conduits and are sizedto maintain a predetermined, approximately constant ratio of flow of theair and gas; a secondary, adjustable restrictor in one of the fuel andair conduits for adjusting the pressure drop across the primary, fixedre; strictor therein; means for supplying air to the air conduit; meansfor supplying fuel to the fuel conduit; means for controlling the fuelpressure entering the fuel conduit in a fixed relation to the pressureof air entering the air conduit; and means for adjusting said secondary,adjustable restrictor in fixed relation to the flow of fluid throughsaid mixture conduit to maintain a constant ratio of flow in said airand fuel conduits for any given amount of total flow.

3. Fluid mixing apparatus for supplying a combustible mixture of fueland air to burners, comprising: an air conduit and a fuel conduitsupplying, respectively, air and fuel to a mixture conduit which in turnis adapted to supply combustible fuel and air mixture to the burners; afirst primary, fixed restrictor in the fuel conduit; a second primary,fixed restrictor in the air conduit, said restrictors restricting flowsin the conduits to maintain their ratio approximately constant forvarying rates of total flow; a secondary, adjustable restrictor in oneof said fuel and air conduits for increasing or decreasing resistance insaid conduit and thereby changing the flow therein; blower means forsupplying air at a substantially constant pressure to the air conduit;means comprising a fuel pressure control valve in the mixture conduit;and connection means for adjusting the secondary, adjustable restrictorresponsive to the position of the mixture flow control valve to maintainconstant ratio of flow in the air and fuel conduits.

4. Apparatus according to claim 3 wherein said primary, fixedrestrictors are venturi shaped.

5. Fluid mixing apparatus for supplying a combustible mixture of fueland air to burners, comprising; an air conduit and a fuel conduitsupplying, respectively, air and fuel to a mixture conduit which in turnis adapted to supply combustible fuel and air mixture to said burners; aprimary, fixed restrictor in each of the fuel and air conduits tomaintain an approximately constant ratio of flow of fuel and air to saidmixture conduit at various rates of total flow; a secondary,pre-adjusted, adjustable restrictor in one of the air and gas conduitsfor changing the resistance in that conduit to maintain a constant ratioof flow of fuel and air to said mixture conduit at varying rates offlow; means for supplying air at a substantially constant pressure tothe air conduit; means for supplying fuel to the fuel conduit at asubstantially constant pressure substantially equal to the pressure ofthe air supplied to the air conduit; :1 mixture flow control valve inthe mixing conduit; and connection means for adjusting the secondaryadjustable restrictor responsive to the position of the mixture flowcontrol valve.

6. Apparatus according to claim 5 in which the secondary, adjustablerestrictor comprises a pre-adjusted adjustable-aperture valve in whichthe aperture area is disproportional to the degree the valve stem isturned.

7. Fluid mixing apparatus for supplying a combustible mixture of fueland air to burners, comprising: an air conduit and a fuel conduitsupplying, respectively, air and fuel to a mixture conduit which in turnis adapted to supply combustible fuel and air mixture to said burners; amixture flow control valve in the mixture conduit; a primary, fixedrestrictor in each of the fuel and air conduits to maintainapproximately proportional resistances and flows in said conduits atvarious rates of total flow; a secondary, adjustable restrictor in oneof the air and gas conduits which is pre-adjusted in fixed relation tothe position of said mixture control valve in a manner to maintain thetotal resistance in that conduit proportional to the resistance in theconduit containing no secondary restrictor, at various rates of flow;means for supplying air at a substantially constant pressure to the airconduit; and means for supplying fuel to the fuel conduit at asubstantially constant pressure substantially equal to the pressure ofthe air supplied to the air conduit.

8. Fluid mixing apparatus for supplying a combustible mixture of fueland air to burners, comprising: an air conduit and a fuel conduitsupplying, respectively, air and fuel to a mixture conduit which in turnis adapted to supply combustible fuel and air mixture to said burners; a

mixture flow control valve in the mixture conduit to adjust the totalflow of the mixture resulting from the mixing of the air and gas fromtheir respective conduits; a primary, fixed restrictor in each of thefuel and air conduits to main approximately proportional resistances andflows in said conduits at various rates of total flow, said restrictorsimparting substantially greater resistance to flow in the conduits thanthe conduits themselves do, whereby the resistances to flow created bysaid restrictors are substantially the only resistances in saidconduits, and said restrictors having such shapes that their resistancesto the flows in said conduits will remain approximately the same for anyrates of flow; a secondary, adjustable restrictor in one of the air andgas conduits which is pre-adjusted in fixed relation to the position ofsaid mixture control valve in a manner tending to maintain the totalresistance in that conduit proportional to the resistance in the conduitcontaining no secondary restrictor, for various rates of flow, wherebythe ratios of the rates of flow will be constant for varying rates oftotal flow; means for supplying air at a substantially constant pressureto the air conduit; and means for supplying fuelto the fuel conduit at asubstantially constant pressure substantially equal to the pressure ofthe air supplied to the air conduit.

References Cited in the file of this patent UNITED STATES PATENTS

